Diademosa Shoemaker & C.E. Babc., Can. J. Bot. 70(8): 1641 (1992).
Saprobic on stems and wood. Sexual morph: Ascomata immersed, initially erumpent becoming superficial, scattered, depressed-globose, some flattened at the base, opening a disc-like lid of brown prismatic cells with setae. Peridium composed of brown pseudoparenchyma cells of textura angularis. Hamathecium of numerous, dense, septate, hyaline, cellular pseudoparaphyses. Asci 8-spored, bitunicate, fissitunicate, clavate with short narrow pedicel and minute ocular chamber. Ascospores biseriate, partially overlapping, fusiform, straight, frequently circular in section but narrowing to one end, with transverse and vertical septa, pale brown to dark brown, smooth walled. Asexual morph: Unknown (Adapted from Ariyawansa et al., 2014).
Type species: Diademosa californiana (M.E. Barr) Shoemaker & C.E. Babc.
Notes: Diademosa is characterised by immersed, initially erumpent ascomata, fissitunicate, clavate asci and partially overlapping, fusiform, pale brown to dark brown, smooth-walled ascospores. The unique distinguishing character of Diademosa is the ascoma opening via a circular lid and ascospores being often circular in section, but narrowing to one end. Barr (1987) introduced Diademosa californiana as Graphyllium californianum and accommodated the genus in Hysteriaceae based on the pore or slit like opening. Shoemaker and Babcock (1992) re-examined the type specimens and assigned Diademosa in Diademaceae based on the morphological resemblance to Diadema mainly the ascomata that opened by a flat lid. Shoemaker and Babcock (1992) reported that the lid is difficult to observe but is ideal to mount it in lactic acid due to extreme swelling in water. Diademosa differs from Comoclathris in having cylindrical, often circular in section, but narrowing to one end ascospores while Comoclathris has flattened ascospores. Diademosa also resembles Pleospora in having narrow, oblong ascomata with cellular pseudoparaphyses and cylindrical to clavate asci with muriform, brown or pale brown ascospores but differs in that Pleospora have ascomata opening by a central pore without setae and asci with a short, thick, furcated pedicel. Diademosa also resembles Pyrenophora in having superficial ascomata with setae and muriform, smooth-walled, light brown to dark brown ascospores but differs in having ascomata opening via disc-like lid. Ariyawansa et al. (2014) placed Diademosa in Pleosporaceae based on morphological similarities with other genera in the family. Diademosa is a distinct genus in Pleosporaceae but fresh collections with DNA sequence data are needed to confirm the taxonomic placement of the genus. Molecular data is unavailable for Diademosa.